Bent plywood



March 23, 1937. Q R, OWENS 2,074,854

BENT PLYWOOD Filed 0G12. 27. 1936 I --llll Patented Mar. I, 23, 1937 UNITED STATES PATENT OFFICE BENT PLYWOOD tion of Illinois Application October 27, 1936, Serial No. 107,810

2 Claims.

My present invention relates to bent plywood and a method employed in making the bend through a. desired curvature. It is commonly desired to produce a bend in plywood so as to form a 5 round corner which is suitable for use in trim, cabinets, furniture pieces of various kinds, etc. By the improvements of this invention I am enabled to perform a bending operation with facility, to complete the operation with a great saving of time, and to provide a bent structure which is ample in strength, which will retain its shape and appearance indenitely, and which is produced with little or no forces of compression to be overcome.

As illustrative of the bent plywood and the method employed, reference may be had to the accompanying drawing, wherein:

, Figure 1 is an edge view of a plywood board in the rst stage of its preparation for the bending operation;

Fig. 2 which is a similar view shows the board in the next stage of its preparation;

Fig. 3 which is an edge view shows the board with the bend completed;

Fig. 4 shows a mechanism suitable for producing the desired bend in the board;

Fig. 5 which is a fragmentary longitudinal section on an enlarged scale shows the board as it appears in the rst stage of its preparation for the bending operation;

Fig. 6 which is a similar view shows the board in the second stage of its preparation; and

Figs. 7 and `8 are views corresponding generally to Figs. 5 and 6, respectively, showing a board of five plies instead of four plies as is elsewhere illustrated.

The board now to be described may be of plywood with a core a of relatively soft wood to one face of which is adhered a cross band b upon 4,0 which is mounted a veneer face c. Applied to the rear face of the core is a back d. 'I'he several plies are arranged preferably with grains crosswise of each other and are united in the usual manner as by layers of glue e.

To prepare the board for the bending operation the back is rst loosened from the core between certain imaginary lines a: and y which deiine the region of the board where a bend is to be made. The back is then slitted between these lines or along one of them, the line :v for example,` a suiicient strip-like part of its body adjacent the line of severance being removed to leave a substantial gap which yinterrupts the continuity of the back. The two spaced edges of the back which dene this gap are designated as ,f and g.

(Cl. 14A-309) It will be understood that the freed portion of the back, including the gap between its facing edges, extends between opposite edges of the board. As shown in Figs. 2 and 6, the back is thereupon left unsupported except in the regions beyond the 5 lines :c and y.

Glue is now applied between the back and core, and, while still unset, a bending force is applied to the board in the region between the lines :c and y. This may be done conveniently with the 10 aid of a die F and a form R. Throughout that portion of the board which is thereupon bent the glue is unset at the time, permitting the back to slide freely, as required, so as to obviate compression. 'I'he initial width of the gap between the 15 back ends f and g may correspond generally with the distance which one or both of these ends of the back will be required to move While taking up a new position during the bending operation. As a result, the gap will be substantially closed so as to restore continuity to the back when the 20 bend is completed (see Fig. 3) The bending force is maintained a suiicient time to allow the glue to set whereupon the bend is permanent and the board may be removed. The back which is the 5 inside ply in the bent board will resist unbending of the board due to its exerting a tension force which counterbalances that of the plies to the outside of the bend.

This method of bending may be employed with 30 a board having three, four, ve or more plies.

A board of four plies has been illustrated and described by way of example. In Figs. 7 and 8 I have shown a five ply board having a second cross band h disposed between the back and core. 35 In preparation for the bend which is to be made it will be desirable, although perhaps not necessary, to produce an interruption in the band as well as the back (see Fig. 8). In such case the cross band is disconnected from the core between 4 the lines a: and y which dene the region of the bend, and the back is also disconnected from the cross band whereby, during the bending opera tion, each of these plies may slide independently, the band upon the core and back, and the back V4f upon the band. At the completion of the bend these two plies will have substantially closed the gap between their ends f and g.

The essence of my invention resides in freeing one or more plies upon the inner side of the board where compressive forces are developed during a bending operation, in cutting out a narrow section of such ply or plies so as to produce a gap or interruption lengthwise thereof,

in applying glue between such ply or plies and 55' the adjacent surface of the board, in applying, while the glue is still unset, a bending force which will produce a sliding movement of the freed ply or plies, thereby avoiding com; resvsion thereof, and in maintaining the bending force until the glue has set. These several steps are requisite with a conventional plywood as now produced, but obviously, if the back be initially applied so that it is already freed in part and/or 10 slitted to provide a gap, then these preliminary steps may be omitted when carrying out the remaining steps of this process.

The number oi plies at the inner side oi' the board which are to be loosened in preparation 15 for bending will depend in large part upon the character and thickness of the board, it being important that so much of the inner board face as would ordinarily be subjected to a compressive force while undergoing bending be loosened and 20 cut away to induce a sliding action. In performing the bend any of the usual expedients may be employed, such as steam, to facilitate shaping of the wood, and heat to accelerate setting of the glue, etc. A resinous glue, either sheet 25 or liquid, will ordinarily be found satisfactory.

I claim: 1. The method ofbending plywood which comprises the steps of applying an unset adhesive between adjacent inner plies the exterior one of which is slitted to provide a gap, and then applying to the plywood in the region of the unset adhesive a bending force which induces sliding of the exterior ply to narrow the gap, the bending force being maintained for a time sufficient to permit the adhesive to set.

2. The method of bending a plywood board which comprises the steps of freeing the outermost ply on the inner face of the board for the entire distance between opposite edges thereof over an area substantially the same as is to be bent, the freed ply remaining elsewhere united y to the board, removing from the ply body a narrow strip extending between opposite edges of the board to provide facing ply edges which deilne a gap therebetween, applying an adhesive between the board and the freed portion of the ply, and then subjecting the board in the region of the freed portion of the ply, while the adhesive is still unset, to a bending force which induces movement of the ply upon the board such that the gap between the ply edges is narrowed, the bending force being maintained for a time sumcient to permit the adhesive to set.

ORVILLE R. OWENS. 

